The invention relates to a storage drum in turning devices of sheet-fed printing machines. Turning devices, operating according to the three-drum turning principle, consist of three sheet-guiding cylinders, the middle one of which is constructed as a storage drum with a diameter, which is twice as large.
The three sheet-guiding cylinders of the turning disposed between two printing cylinders. Such a turning device enables the sheet to be turned according to the sheet rear edge turning principle and, with that, the sheet to be printed in one passed.
A sheet-guiding cylinder of normally single diameter precedes the storage drum and the turning drum with a single diameter follows it.
In each case, the storage drum has two sheet holding systems for the front and to rear regions of the sheet. The sheet holding systems for the front region and the sheet holding systems for the rear region are diametrically opposite to one another.
Changeover manipulations must be carried out when changing the mode of operation from recto to recto and verso printing or vice versa or when processing sheets of a different length by recto or recto and verso printing. For adjusting the sheet holding systems for processing sheets of different length, it is necessary to adjust the sheet holding systems for the front and rear regions relative to one another
The publication DE 39 116 30 C2 discloses an arrangement of sheet-holding systems at a storage drum. The sheet-holding system for the front region of the sheet, which is constructed as a clamping gripper, is permanently disposed at the body of the storage drum. The sheet-holding system for the rear region of the sheet, constructed as a suction device, is provided at a supporting element, which is disposed detachably at the body of the storage drum.
The supporting element and, with that, the suction device provided at the supporting element can be adjusted in the circumferential direction by means of an adjusting shaft, which is mounted in the drum shaft. A motor for actuating the adjusting shaft is disposed over a gear wheel step at one end of the adjusting shaft (on the outside) and a pinion is disposed at the other. The pinion engages a toothed segment, which is connected with the supporting element. The adjusting shaft is mounted eccentrically in the drum shaft.
If it is necessary to adjust the sheet-holding systems relative to one another in the circumferential direction of the storage drum, the adjusting shaft, which acts over the pinion and the toothed segment on the supporting element, is rotated by means of the motor and the gear wheel step. The suction devices are shifted with the supporting element relative to the clamping gripper.
The large expenditure for parts is a disadvantage of such an adjusting device of the sheet-holding systems. Many gearing elements engage one another with clearance, so that the adjustment of the sheet-holding systems to the dimensions of the sheet, which is to the processed, is inaccurate. The drilling and milling in the drum shaft leads to a weakness in the drum leg.
The DE 39 008 18 C1 shows a sheet-guiding drum with an inner shaft and an outer drum with at least one segment, which can be adjusted in the circumferential direction with respect to the inner shaft. The sheet-holding systems are assigned to the inner shaft and the outer drum, which are coupled together by means of a multiple-plate coupling.
The clutch is between an end surface of the segments and a journal pin of the shaft. The clutch can be actuated over a tie rod and a clamping lever, which can be actuated from the outside and, with that, the connection between the shaft and the segment can be undone. After that, both can be adjusted relative to one another with the sheet-holding systems.
The large expenditure for parts is a disadvantage of this fixing and loosening device. Access to the clutch within the bearing of the sheet-guiding cylinder for maintenance work in the event of wear and contamination is difficult. In this case also, the drilling and milling leads to a weakness in the leg.
Starting out from this state of the art, it is an object of the invention to change the relative angular position of the sheet-holding systems to one another at a storage drum in turning devices with little expenditure and simple means.
Pursuant to the invention, this objective is accomplished by the distinguishing features as claimed.
The inventive solution has the advantage that, with little expenditure for the recto printing or for the recto and verso printing, the sheet-holding systems on a storage drum can be adjusted relative to one another in the circumferential direction and locked once again. This is made possible by a clutch, which lies outside of the storage drum.
An oil-under-pressure connection, which can be used in an advantageous manner for the phase shift in the case of a change in the mode of operation or when processing a different format in recto and verso printing, is used to undo the connection of a double gear wheel.
Between the two sheet-holding systems-gripper system for the sheet in the front region and the suction system for the sheet in the rear region, there is a clutch, which can be released by an oil-under-pressure connection by pressing oil into the press fit, after which the sheet-holding systems can be shifted relative to one another.